Back handspring tips?

i've been working on my back handspring and i always psych myself out! i am capable of doing it pretty well i just always get scared im gonna hit my head or get hurt or something! i am on a really good cheer mat and a coach is there telling me i can do it it's just always in the mind set! how do i not psych myself out?! im 14 and want to get my back handspring and eventually my back tuck by the end of the summer for cheerleading in the fall! also, any tips on form?